Electron-discharge device



July 24, 1928.

M. J. KELLY ELECTRON DISCHARGE DEVICE Filed July 8, 1924 Patented July 24, 1928.

; UNITED STATE-S PATENTFOFFI'CE.

1 mvm J. 'mmz, or new YORK, 11. Y., assrenon rowns'rm'nnncrmc comm, mconrom'mn, or New xoax, n. 1., A oonrom'rron or new Yonx.

ELECTRON-DISCHARGE DEVICE.

a puoauon'm a m a, 1924. Serial no. ream.

This invention relates to electron discharge devices and has for an object a low impedance device of this character having a high amplification factor in which the electron. emitting element may be energized by alternating current.

. This obJect is attained b utilizing as 'a cathode a thermionically active member havmg a large active surface and energizing this member by means of a heating element separate therefrom. For the thermionically active member there is provided a; metallic cylinder coated with alkaline earth oxides. Associated with this cylinder is an electric resistance element b means of which heat is applied to the cylinder to activate the oxides. A control electrode surrounds the cathode and comprises a helical wire grid.

The surface of the grid wire is oxidized in order to prevent its becoming thermionically active due to the deposition of a layer of alkaline earth oxides vaporizedthereon from cathode is a cylindrical anode, which is comthe cathode. Surrounding the grid and posed of decarbom'zed nickel to prevent the reduction ofthe oxide coating of the grid during the evacuation of the tube by carbon supplied from the anode.

- By virtue of the geometric arrangement of t e electrodes and the large active cathode surface, the impedance of this device is very low and its. space current correspondingly high. As a result the amplification factor can be made much higher forthe same output impedance than electron discharge devices of corresponding s'ize having filamentary cathodes. Moreover, the cathode has the same potential throughout its surface and the voltage drop between itand the anode is, therefore, uniform. .Alternating current may besupplied tofthe heating tion of the tube,

element to activate the cathode. without in-1' troducing any disturbances into thei f'ope'ra- Fig.2 discloses the heating unit and Fig. 3

since there is no current flow'inthe cathode itself.

" Referi'ing now to the drawin discloses. an electron discharge eviceconstructed in accordance with the invention.

discloses the heating unit combined with the cathode.

The enclosing vessel 10 of the device is provlded with an inwardly proiectin stem 11. A pair of rods 12 are sealed in t e end of the stem 11 and extend longitudinall of the tube, their ends bein seated in a block 13 of insulating materia preferably of the material commercially known as "lavite. A rod 14 is also sealed in the stem midway between the rods 12 and extends through the block 13 its free end being slidable 1n the block. Supported on the rod 14 is a core or spool 15 of refractory material having a e echigh thermal conductivity and a low trical conductivity. As shown in Fig. 2, a

filament 16, preferably of tungsten wire, is I wound around the spool. The wire 16 is covered with a coating 17 of alundum ce-' ment. Surrounding the spool 15 and supported thereby is a metallic cylinder 18,

preferably of nickel, which is coated with a thermiomcally active material. This coating preferably is composed of a mixture of strontium and barium oxides. One end of the filament 16 is weldedto the rod 14 at 19 and the other end is connected to the lead-.

ing-in wire 20.. A leading-in wire 21 is atv tached to the opposite end of the rod 14- whereby heating current may be supplied to the filament 16. A leading-in wire 22 is provided for the cathode 18;

Surrounding the cathode is a grid or con 7 trol electrode 23 which comprises a pairof longitudinal rods or wires 24 betweenwhich ishelically wound a lateral wire25. .---Both the rods 24 'a nd the wire 25 arecomposed-Of nickel or'an alloy thereof. which hasgbeeni oxidized to form on the surfaceia coating i of nickel oxide. One ofthe rods 24 isweld ed to a leading-in wire 26 which also serves as a. supporting wire, and the-oppositev end of this rod together with the corresponding end of the other rod 24 is slidablymounted in theinsulating block 13.

The anode 27 comprises a metallic cylinder supported between the rods 12 by means ofthe referably nic el, from which all'carbon has members 28 and surrounds the other elemerits. This 0 linder is composed of a metal,

' een removed for a considerable" depthfrom the surface. A leading-in wire for the joined to the end of one of the not removed from the anode it reacts with water vapor and oxygen within the tube to form carbon monoxide. Carbon monoxide, if present in the tube, reduces the oxide coating on the grid to give a clean grid surface. Depositions on the clean grid surface of alkaline earth oxides from the cathode render these portions of the grid thermionically active. The water vapor above mentioned comes from the glass envelope of the device and from the electrodes. The oxygen comes from the same parts and probably from the reduction of the alkaline earth oxide coating on the cathode. There is usually so much water vapor and oxygen within the containing vessel of the device that sutficient carbon monoxide is formed to reduce the oxide coating of the grid to such an extent that enough alkaline earth oxides are deposited on bare spots thereon to render the grid so active ther- -mionically as to prevent proper operation of the device. Also, the long continued reaction between the carbon and water vapor and oxygen destroys to a large extent the activity of the cathode. However, the use of an anode of decarbonized nickel prevents the formation of carbon gases and permits the device to be evacuated quickly and without redziiction of the nickel oxide coating of the grl Because of the comparatively large surface areaof the cathode, the spacecurrent between it and the anode is very large and the device has a high amplification factor. It is, therefore, possible to obtain greater degrees of amplification with corresponding plite voltages than has heretofore been possi le.

It is, of course, understood that various modifications may be made in the structure and arrangement of the various elements ofv the device above described without in any way departing from the spirit of the invention, as set forth in the appended claims.

The invention claimed is: n

1. An electron discharge device comprising an enclosing vessel having a re-entrant stem, a pair of rods extending from said stem, a block of insulating material joining the free ends of said rods, another rod having one end sealed in said stem and the other end slidably mounted in said insulating block, a heating element insulatingly supported on said rod, a metallic cylinder surrounding said heatin element and insulatingly supported there y, a grid element supported from'said stem and said insulating block, and a cylindrical anode surrounding said other elements and'supported from said first two rods.

2. An electron dischar e device comprising a metallic rod, a spoo of refractory material carried thereby, a metallic cylinder supported by said spool, said cylinder hav-- ing a thermionically active surface, and an electric resistance embedded in said spool.

3. An electron discharge device comprising an enclosing vessel having a stem a metallic rod sealed in said stem, a leading-in wire for said rod, a spool of refractory material carried by said rod, a c linder havin a thermionically active sur ace supported by said spool, a resistance element embedded in said spool and having one end connected to said rod, and a leading-in wire connected to the opposite end of said resistance element.

4. An electron discharge device comprising a vessel having a stem, a plurality of rods sealed in said stem, at block of insulating material connecting the free ends of said rods, the end of one rod bein slidable in said block, a thermionically active member supported by said last named rod, a metallic cylinder supported by said other rods, and leading-in wires connected to certain of said rods.

5. An electron discharge device comprising an enclosing vessel having a stem, a pair of rods sealed in said stem, a leading-in wire for one of said rods, a block of insulating material joining together the free ends of said rods, another rod sealed in said stern and having its free end slidably mounted in said insulating block, a leading-in wire for said rod, an electrical heating unit carried by said rod and having one end connected thereto, a leading-in wire'for the other end of said heating unit, a thermionically active cylinder supported by said heating unit, a grid electrode surrounding said cylinder and being slidably supported by said block of insulating material, and a cylindrical anode surrounding said grid and supported by said first two named rods.

6. A cathode for electron discharge devices comprising an electrical conductor, a spool of electrically non-conductive material havinghigh thermal conductivity carried by said conductor, a filamentary conductor wound on said spool and having one end connected to said first conductor, a layer of electrically non-conductive cement covering said filamentary conductor, and a thermionically active cylinder surrounding said spool and supported thereby.

7. An electron discharge device comprising an enclosing vessel having a stem, a pair v a metallic member sealed in said stem, said of metallic rods sealed in said stem and hav grid electrode and said last named rod being ing their free ends connected by a block of slidably connected to said insulating block. 10 insulating material, a cylindrical anode sup- In witness whereof, I hereunto subscribe 5 ported by said metallic rods, a thermionicalmy name this 2 day of July A. D., 1924.

ly active member supported by a rod sealed in said stem, a grid electrode supported by MERVIN'J. KELLY. 

